The present invention relates to an expansion valve used in a refrigeration cycle such as an air-conditioning apparatus or a refrigeration apparatus, and a method of producing the expansion valve.
A thermal expansion valve is used in a vapor-compressing refrigeration cycle. The thermal expansion valve decompresses and expands high-pressure refrigerant in a manner that a superheat degree of refrigerant flowing out of an evaporator becomes close to a predetermined value. This kind of expansion valve includes an element portion to be displaced in accordance with a temperature and a pressure of refrigerant flowing out of the evaporator. A valve portion is displaced by the displacement of the element portion, such that an opening degree of a throttle passage to decompress and expand high-pressure refrigerant is controlled.
Specifically, the element portion includes a diaphragm corresponding to a pressure-responding part, which is displaced in accordance with a pressure difference. The pressure difference is defined between an inner pressure of a seal space filled with a temperature sensing media and a pressure of refrigerant flowing out of the evaporator. A pressure of the media is varied in accordance with the temperature. The displacement of the diaphragm is transmitted to the valve portion through a temperature sensing bar. The bar transmits a temperature of refrigerant flowing out of the evaporator to the media.
Thus, the pressure of media filled in the seal space corresponds to the temperature of refrigerant flowing out of the evaporator. The diaphragm is displaced based on the pressure difference between the inner pressure of the seal space and the pressure of refrigerant flowing out of the evaporator. JP-B2-3995828 discloses an expansion valve, in which an opening degree of a throttle passage is controlled by displacing a valve portion. The valve portion is displaced by a displacement of a diaphragm in accordance with a temperature and a pressure of refrigerant flowing out of an evaporator.
This kind of thermal expansion valve typically includes a body portion to form an outer frame, and the body portion has a refrigerant passage through which high-pressure refrigerant passes, a throttle passage to decompress and expand the high-pressure refrigerant, and another refrigerant passage through which refrigerant flowing out of an evaporator passes. Further, a temperature sensing bar and a valve portion are arranged inside of the body portion, and an element portion is arranged outside of the body portion.
Therefore, when outside air temperature is low in winter, temperature sensing media filled in a seal space of the element portion condenses. That is, the media is in an overcooled liquid state.
In this case, because the seal space is difficult to have a pressure variation, the pressure of the seal space cannot correspond to the temperature of refrigerant flowing out of the evaporator. As a result, malfunction may be generated, because the valve portion cannot properly control the opening degree of the throttle passage.
JP-A-H09-159324 discloses a gas-charged expansion valve as a decompressing device of a refrigeration cycle. Gas phase temperature sensing media is filled in a temperature sensing portion of the expansion valve. Resin having low heat conductivity is inserted around an outer circumference of a temperature sensing bar. The bar is made of aluminum, and corresponds to a stem defining a valve driving bar. The resin is tightly integrated with the temperature sensing bar, and may be made of PPS resin, for example, having no over-time change generated by refrigerant.
A part of the temperature sensing bar is exposed to a low-pressure refrigerant passage through which gas phase refrigerant of a refrigeration cycle passes, and the resin in arranged on the exposed part. A temperature of vapor refrigerant flowing through the low-pressure refrigerant passage out of the evaporator is transmitted to refrigerant filled in an upper pressure-responding chamber of a power element as a temperature sensing fluid. Thus, operating gas having a pressure corresponding to the transmitted temperature is generated. Therefore, even when non-vapor low-pressure refrigerant flows out of the evaporator into the low-pressure refrigerant passage and adheres on the resin, a time constant of heat transmission becomes large, because the resin has the low heat conductivity. Thus, responding characteristic of the expansion valve becomes insensitive. Therefore, if the evaporator has a rapid change of thermal load, the refrigeration cycle can be restricted from having a hunting phenomenon, because the responding characteristic of the expansion valve is insensitive.
Further, JP-A-2001-33123 discloses an adsorbent-charged expansion valve. An upper pressure-responding chamber of a power element and a hollow part of a temperature sensing bar communicate with each other so as to define a space filled with operating fluid. Adsorbent such as activated carbon is arranged in the hollow part, and pores of the adsorbent have diameters corresponding to a molecular diameter of the operating fluid. A lower pressure-responding chamber of the power element communicates with a low-pressure refrigerant passage through a clearance defined around the temperature sensing bar. A temperature of vapor refrigerant flowing through the low-pressure refrigerant passage out of the evaporator is transmitted to the operating fluid of the hollow part. Thus, a pressure corresponding to the transmitted temperature is transmitted to the operating fluid of the upper chamber.
Therefore, a diaphragm of the power element drives the bar based on a pressure difference defined between a gas pressure of the operating fluid in the upper chamber and a vapor pressure of refrigerant at an outlet of the evaporator. Thus, an opening degree of an orifice is controlled by a valve portion, such that a flowing amount of liquid refrigerant into an inlet of the evaporator is controlled.
Due to the activated carbon arranged in the hollow part of the bar, it takes a time to hold a balance of temperature and pressure between the activated carbon and the operating fluid. Therefore, controlling characteristic of the refrigeration cycle becomes stable, and a hunting phenomenon can be restricted from being generated.
JP-A-H09-159324 discloses an expansion valve, in which a resin layer is arranged around an outer circumference of a temperature sensing bar. Heat is transmitted from gas phase low-pressure refrigerant flowing through a low-pressure refrigerant passage, and the heat transmission is delayed by the resin layer. Thus, a time constant can be increased. However, influence of heat transmission from outside air or the expansion valve becomes relatively large relative to sealed refrigerant, because the heat transmission from the low-pressure refrigerant is made low. In this case, a temperature of the bar becomes higher than a temperature of the low-pressure refrigerant. Therefore, temperature detected by the bar may have errors in a steady time when refrigerant has a stable temperature and a constant pressure.
The hunting phenomenon is generated by an interaction between a responding delay of the expansion valve and a responding delay of the cycle. The responding delay of the expansion valve is generated, because a controlling of an opening degree of an orifice corresponding to a decompressing portion is delayed from a detecting of a temperature of refrigerant flowing through an outlet of an evaporator. Therefore, when the responding delay (time constant) of the expansion valve is made sufficiently larger than the responding delay of the cycle, the hunting phenomenon can be reduced. However, the responding delay of the cycle is changed by a variation of a flowing amount (flowing speed) of refrigerant, when an air-conditioning load is changed. In a case that the expansion valve is designed to have a sufficiently large time constant in a condition that the flowing speed of refrigerant is low, the responding delay becomes too large in a condition that the flowing speed of refrigerant is high. Thus, the cycle cannot have a proper operation.
Further, the temperature of the sensing bar is affected by heat transmitted from the diaphragm, because the diaphragm is affected by atmospheric temperature of the expansion valve. Furthermore, because refrigerant is sealed above the diaphragm, temperature distribution may be generated in the longitudinal direction of the sensing bar. Due to the temperature distribution, when the atmospheric temperature is high, for example, refrigerant sealed in the upper chamber may have a temperature higher than a temperature of low-pressure refrigerant flowing through the low-pressure refrigerant passage. In this case, a valve-opening operation may be erroneously performed as malfunction.
JP-A-2001-33123 discloses an expansion valve, in which activated carbon is arranged in a hollow part of a temperature sensing bar. Due to the activate carbon, operating fluid has a time constant to perform a direct heat transmission. The operating fluid is adsorbed on the activated carbon, and is introduced toward the low-pressure refrigerant passage. Thus, an error of the detected refrigerant temperature becomes small. However, cost and man-hour are increased for filling the activated carbon in the hollow part, such that productivity may become worse.
Further, because the operating fluid is adsorbed on the activated carbon, the pressure of the upper chamber is increased in accordance with a temperature increase. In this case, the expansion valve cannot have a MOP (maximum operating pressure) characteristic. When the operating fluid in the seal space is heated to have gas phase, the pressure increasing of the upper chamber becomes slow, in a case that the expansion valve has the MOP characteristic. Thus, power needed for driving a compressor can be reduced at a high load time.
Further, a liquid-charged expansion valve is known as a decompressing device, in which gas-liquid mixture state temperature sensing fluid is filled in a temperature sensing portion. Similarly to JP-A-2001-33123, the liquid-charged expansion valve cannot have the MOP characteristic, because the temperature sensing fluid has a gas-liquid mixture state at a using time. Further, the producing cost is high, because a diaphragm of a power element is required to withstand a high pressure applied at a high pressure time. Further, the productivity of the liquid-charged expansion valve is low due to high cost and large man-hour, compared with the gas-charged expansion valve.